1. Field of the Invention
This invention relates generally to an apparatus and method for shoulder arthroplasty and, more particularly, to a humeral component and other associated surgical components and instruments for use in shoulder arthroplasty.
2. Discussion of the Related Art
A natural shoulder joint may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace a natural shoulder joint with a prosthetic shoulder joint. When implantation of such a shoulder joint prosthesis becomes necessary, the natural head portion of the humerus is resected and a cavity is created in the intramedullary canal of the host humerus for accepting a humeral component. The humeral component includes a head portion used to replace the natural head of the humerus. Once the humeral stem component has been implanted, the humeral head is sized and positioned at the scapula head to ensure proper movement. The glenoid may also be resurfaced and shaped to accept a glenoid component. The glenoid component generally includes an articulating surface which is engaged by the head portion of the humeral component.
It is generally known in the art to provide a shoulder joint prosthesis having a humeral component, as discussed above. However, the current prior art humeral components along with the associated surgical components and instruments utilized during shoulder arthroplasty suffer from many disadvantages.
For example, since the humeral component is subject to various types of loading by the surface of the glenoid component, the humeral component must offer a stable and secure articulating surface. To achieve this, the humeral components provide stems which are inserted into a hole bored into the intermedullary canal. However, such existing stemmed humeral components also exhibit several disadvantages. For example, some of the stemmed humeral components utilize single centered stems of various sizes to stabilize and secure the humeral component to the humerus. While the hemispherical radius of the head can be adjusted to compensate for differences in the stem size, use of such an adjusted head radius does not always provide proper spacing and allow proper joint articulation since the articulation axis of the head does not change with the change in head size. To overcome this, a myriad of designs offer heads having offset pegs and sleeves, thus increasing the complexity of the surgery. Furthermore, the offset head designs require heads having varying hemispherical shape in conjunction with the sleeves to allow for a proper joint functioning.
As shown in FIGS. 1a and 1b, most prior art humeral components rely on stems 100 having a single fixed offset from the proximal end of the stem. The heads 102 to be coupled to the stems 100 are situated so that the articulating surfaces 104 and 104′ are parallel. In instances where the head 102 has a large diameter, a portion of the head 102 overlaps the longitudinal axis a significant amount. This is an undesirable condition which leads to improper joint kinematics. The stems 100 may also include extensions which act to anchor the stem within the intermedullary canal once the stem is cemented within the humerus. The proximal end of most humeral components are, thus, generally overlooked to enhance the articulation and are, therefore, generally standardized.
What is needed then is a humeral component and associated surgical components for use in a shoulder arthroplasty which does not suffer from the above-mentioned disadvantages. This in turn, will provide a humeral component which is stable and secure, reduces the overall amount of bone tissue required to be removed, reduces the overall surgical time and complexity, increases overall joint articulation, and enhances and increases natural articulation without increasing overall component count. It is, therefore, an object of the present invention to provide such a humeral component and associated surgical components for use in shoulder arthroplasty.